Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.
Nature. 2013 Oct 10;502(7470):201-6. doi: 10.1038/nature12578. Epub 2013 Oct 2.
Na(+),K(+)-ATPase pumps three Na(+) ions out of cells in exchange for two K(+) taken up from the extracellular medium per ATP molecule hydrolysed, thereby establishing Na(+) and K(+) gradients across the membrane in all animal cells. These ion gradients are used in many fundamental processes, notably excitation of nerve cells. Here we describe 2.8 Å-resolution crystal structures of this ATPase from pig kidney with bound Na(+), ADP and aluminium fluoride, a stable phosphate analogue, with and without oligomycin that promotes Na(+) occlusion. These crystal structures represent a transition state preceding the phosphorylated intermediate (E1P) in which three Na(+) ions are occluded. Details of the Na(+)-binding sites show how this ATPase functions as a Na(+)-specific pump, rejecting K(+) and Ca(2+), even though its affinity for Na(+) is low (millimolar dissociation constant). A mechanism for sequential, cooperative Na(+) binding can now be formulated in atomic detail.
Na(+)、K(+) - ATPase 酶每水解一个 ATP 分子，就将三个 Na(+) 离子从细胞内泵出，同时将两个从细胞外介质中摄取的 K(+) 离子交换进来，从而在所有动物细胞中建立起跨膜的 Na(+) 和 K(+) 梯度。这些离子梯度被用于许多基本过程，特别是神经细胞的兴奋。在这里，我们描述了来自猪肾的这种 ATP 酶与结合的 Na(+)、ADP 和铝氟化物（一种稳定的磷酸盐类似物）以及促进 Na(+) 封闭的寡霉素的 2.8Å 分辨率晶体结构。这些晶体结构代表了一个过渡态，在此之前是磷酸化中间产物（E1P），其中三个 Na(+) 离子被封闭。Na(+) 结合位点的细节显示了这种 ATP 酶如何作为一种 Na(+) 特异性泵发挥作用，排斥 K(+) 和 Ca(2+)，尽管它对 Na(+) 的亲和力很低（毫摩尔解离常数）。现在可以用原子细节来描述顺序、协作的 Na(+) 结合的机制。
